3-Level Asymmetric Full-Bridge Soft-Switched PWM Converter for 3-Phase Unfolding Based Battery Charger Topology

In this paper, the authors propose a new topology referred to as 3-Level Asymmetric Full Bridge (3LAFB) for back-end isolated DC-DC stage required in three-phase rectifiers based on unfolding approach. The three-phase unfolding based approach improves the power density and efficiency of the converter for isolated battery charging applications. The DC-DC stage used in this approach is usually implemented by two separate converters for processing different time-varying power from each of the two soft DC links. The authors propose a single 3-level DC-DC converter that can simultaneously process power from both the soft-dc links. This results in further reduction in size of the converters based on unfolding approach. Modulation strategy is also proposed for this 3LAFB topology such that the conduction duration of the 4-quadrant switches are minimized and all the active devices soft-switch. With the proposed modulation, converter has the ability to process different powers from each of the DC links that are required to maintain power factor correction (PFC) action on the grid side. Ideal converter simulation waveforms are used to explain the operation of the converter. Hardware results from a 2 kW prototype are presented at three different operating conditions that cover the full voltage range at the input. The results provided validate the proposed converter ability to meet the requirements of the DC-DC stage in an unfolding rectifier.